I couldn't handle such a rule in a serious relationship but maybe it would be okay for a more casual connection. Try doing a tag search for Don't Ask Don't Tell or DADT for other perspectives.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.